Electroluminescent displays are gaining popularity for use in displaying alphanumeric text and other matter. This type of display can be a thin film sandwiched unit, having orthoginal arrays of row and column lines. The intersection of an addressed row and column line causes the adjacent luminescent material, or pixel, to become illuminated. By selectively addressing the array row and column lines, alphanumerics can be displayed.
An inherent characteristic of electroluminescent displays is a requirement for a high driving voltage, which may be as high as several hundred volts. An additional requirement is that such a display must be driven by a signal which exhibits an AC component. The AC signal component assures that the display pixels adjacent the array intersections, which are capacitive in nature, do not retain a residual charge when not driven.
Semiconductor driver circuits tailored for driving electroluminescent displays must therefore be able to withstand high voltages, with currents sufficient to charge or discharge the capacitive pixels of the display. Circuits adapted for driving the rows of an electroluminescent display are identified as integrated circuit types SN75552, manufactured by Texas Instruments Incorporated. The noted row drivers include an N-channel double diffused field effect transistor (DMOS) as the device for driving the row lines of electroluminescent displays. In order to supply the requisite current, which may be in the neighborhood of 100 milliamp, the channel width of the FET device must be rather large, in the neighborhood of about 70-80 mils. To accommodate a requisite 225 volt breakdown voltage, the DMOS transistor requires a total of about 300 square mils of wafer area. This represents a substantial chip area, which reduces the number of chips that can be fabricated on a semiconductor slice or wafer. Because of the wafer area required of these conventional DMOS row drivers, the cost disadvantage thereof presents an impediment to the further acceptance and widespread use of electroluminescent displays.
From the foregoing, it can be seen that a need exists for an improved electroluminescent driver which requires less wafer area, without reducing the current drive or voltage breakdown capabilities, so that additional chips can be formed on a wafer. By increasing the number of chips fabricated on a wafer, the process yield increases and the cost of fabrication is reduced.